Where possible, use the newly registered image size. The original image
size will be available to call on for backup, for images uploaded prior
to WordPress 5.3.
WordPress is adding new image sizes in version 5.3, so our custom image
size is redundant. Keeping it in for back compat, plus older images
will still need to be retrieved using the old image size name, or else
the original size will be used in lieu of a correctly sized option.
Robin Cornett